N-1,3-Dimethylbutyl-N{40 -1,4-dimethylpentyl-p-phenylenediamine antiozonants

ABSTRACT

N-1,3-Dimethylbutyl-N&#39;&#39;-1,4-dimethylpentyl-p-phenylenediamine useful for the preservation of rubber.

United States Patent [191 Summers Dec. 30, 1975 [5 N- l,S-DIMETHYLBUTYL-N 1 ,4-

DIMETHYLPENTYL-P- PHENYLENEDIAMINE ANTIOZONANTS [75] Inventor: CharlesGene Summers, Medina,

Ohio

[73] Assignee: Monsanto Company, St. Louis, Mo.

[22] Filed: Oct. 10, 1974 [21] App]. No.: 513,712

[52] US. Cl. 260/45.9 QB; 260/814; 260/577 [51] Int. Cl. C08G 6/00 [58]Field of Search 260/814, 45.9 QB

Primary ExaminerV. P. Hoke [57] ABSTRACT N-l ,3-Dimethylbutyl-N '-1,4-dimethylpentyl-pphenylenediamine useful for the preservation ofrubher.

3 Claims, No Drawings N-1,3-DIMETHYLBUTYL -N'- I,4-D IMETHYLPEN-TYL-P-PI-IENYLENEDIAMINE ANTIOZONANTS;.

This invention relates to theunsymmetrical dialkyl-pphenylenediamine, 1,3-dimethylbutyl-l ,4-dimethylpentyl-p-phenylenediamine and to .diene.elastomer compositions preserved therewith.

BACKGROUND OF THE INVENTION Certain unsymmetricaldialkyl-p-phenylened-iamines are known. For example, certainunsymmetrical dialkyl-p-phenylenediamines in which one alkyl is derivedfrom an aldehyde and the other from a ketone are described in US. Pat.No. 3,504,032 and test results described which indicate that theypossessantidegradant activity for diene elastomers comparable to that ofthe symmetrical N',N-di(sec-alkyl)-p-phenylenedia mines having 7 or 8carbon atoms in each alkyl group which have become widely accepted inthe rubber industry. However, reaction with aldehydes is difficult tocontrol and leads to excessive by-product formation. Moreover, therequirements of low volatility and high degree of safety to workmencoming in contact with either the antidegradant or preserved rubber areseverely limiting of practically usable antidegradants.

SUMMARY OF THE INVENTION It has been found thatN-l,3-dimethylbutyl-N'-1,4- dimethylpentyl-p-phenylenediamine is avaluable, improved antidegradant for diene elastomers. It impartsunusually high resistance to degradation of diene elastomers by ozoneunder'both static and dynamic conditions. Waxes provide significantprotection from ozone under static conditions but antidegradants arerequired to supplement the static protection and to provide protectionunder conditions inwhich the elastomer is strained or continually.flexed. The discovery of the new compound and its valuable properties isfurther significant because it is derived in part from the readilyavailable methyl isobutyl ketone.

DESCRIPTION OF PREFERRED EMBODIMENTS The new compound is obtainable bycondensing methyl isoamyl ketone with p-nitroaniline to form the anilintermediate, reducing theanil to N-1,4-dimethylpentyl-p-nitroanilineand condensing it with methyl isobutyl ketone under conditions forreductive alkylation. To prepare the N-l,4-d imethylpentyl;pnitroanilineintermediate, 138 parts by weight 1,molecular proportion) ofp-nitroaniline, 120 parts by weight (1.05 molecular proportions) ofmethyl: isoamyl ketone, 7 parts by weight of acidic carbon blackcatalyst(Summers US. Pat. No. 3,414,616) andabout 175 parts by weight of xyleneare charged to'a suitable reactor and the mixture heated at refluxingtemperature (144-153C) for about 2% hours during which time a portion ofthe xylene and a little water is removed. There is then added 1 part byweight of salicyclic acid and heating continued at refluxing temperature(153C) for about 8 hours while collecting parts by weight of water.There is then added 100 parts by weight of methyl isoamyl ketone andheating continued at 153 C until a total of 18 parts by weight of waterhave been removed. The reaction mixture is stripped of solvent, 240parts by weight of alcohol added and the resulting solution added to aslurry of 28 parts by weight of sodium borohydride (NaBH in about 240nitrochlorobenzene parts by weight of ethyl alcohol at 50C. A solutionforms which is stirred for about 3 hours at 3050C, filtered and thesolvent removed from the filtrate by distillation. Xylene is added andthe xylene solution washed with water and most of the xylene removed invacuo.

To conduct the next step, 3 molecular proportions (300 parts by weight)of methyl isobutyl ketone, 1 molecular proportion ofN-1,4-dimethylpentyl-pnitroaniline in xylene prepared as describedabove, 8 parts by weight of 1% platinum on carbon and 8 parts by weightof acidic carbon co-catalyst are charged to a suitable reactor.Reduction of the nitro group is effected at C, 14.06 kg/sq cm hydrogenpressure '(200 lbs/sq in). The temperature is then increased to about Cand the hydrogen pressure to 28.284 kg/sq cm. After about 2 hours, thepressure is released and the reaction mixture cooled, filtered, waterremoved from the filtrate by distillation and the residue fractionatedin vacuo collecting anamber liquid, b.p. 200-205C at 2-3 mm Hg pressure.

In another and preferred embodiment, N-l,3-dimethylbutyl-p-nitroanilineis prepared by condensing pwith 2-amino-5-methylhexane. Into anautoclave is charged 1 17 parts by weight (0.75 molecular proportion) ofp-nitrochlorobenzene, 258 parts by weight (2.25 molecular proportions)of 2- amino-S-methylhexane and 40 parts by weight (2.25 molecularproportions) of water. The charge is heated at 158172C for about 15hours at a pressure of 6.79-7.03 kg/sq cm until the p-nitrochlorobenzenehas essentially disappeared-The resultingN-1,3-dimethylbutyl-p-nitroaniline is then alkylated as follows:

A hydrogenator is charged with 116 parts by weight (0.5 molecularproportion) of N-1,3-dimethylbutyl-pnitroaniline, 200 parts by weight(2.0 molecular proportions) of methyl isobutyl ketone, 10 parts byweight of 1% platinum on carbon catalyst (50% wet) and .2 parts byweight of acetic acid. The charge is heated at 100C under 28.12 kg/sq cmhydrogen pressure for 4 hours, filtered and the filtrate stripped ofvolatiles by heating to 180C/5 mm Hg pressure. The residue is distilledcollecting N-l ,3-dimethylbutyl-N'-1,4-dimethylpentyl-p-phenylenediamine, b.p. C/1 mm Hg pressure.

Rubber ozone resistance data for the product of this invention isillustrated by a method published by Decker and Wise, The StressRelaxation Method for Measuring Ozone Cracking, Rubber World, April1962, page 66. The equipment comprises an oven serving as an ozonecabinet filled with ozone generating equipment and racks for both staticand dynamic testing. Static racks handle stocks at strains of 5, 10, 20,30 and 40%. The dynamic rack is a reciprocal mechanism which imparts a25% strain to the rubber test piece on movement of a top plate whichmoves vertically with respect to a stationary bottom plate. Themechanism is driven at a rate of 90 cycles per minute by a gear mountedon the outside, of the cabinet. The test pieces are 2-inch long T-50(ASTM D599-55) specimens died from standard stress strain test sheets(ASTM D15- 57T). They are mounted by placing the ends in radial slotsmilled into the edges of circular plates of the racks. The tab ends fitinto circumferential grooves machined into the outer surfaces of theplates.

The stress relaxation method is based on the principle that theeffective cross-sectional area of a small test piece of rubber isreduced by ozone cracking. The

3 extent of cracking in a test piece is determined by measuring theforces required to extend the test piece 100% before and after exposureto ozone. The ozone concentration for the test is 25 parts ozone/ l00.million 4 N,N '-di( 1 ,4-dimethylpentyl )-p-phenylenediamine. Stockcontains symmetrical N,N'-di( 1,4-dimethylpentyl)-p-phenylenediamine.Static ozone tests of only a few of the stocks falls to a 90% level sothat the stocks parts air. As the strip begins to crack, the number of 5cannot be compared by the aforedescribed method.

stress supporting rubber chains decreases and the force required toextend the strip 100% is reduced. The ratio of this force to theoriginal force is calculated at approximately 16-hour intervals ofexposure to ozone. The graph of force vs. time is essentially a straightline and the time required for obtaining 90%, 80% and 70% respectivelyof the original force is determined from the graph. The ability of therubber to resist ozone attack is evaluated by comparison of these timesto times for suitable controls to reach corresponding percent of theoriginal force. The percents of original moduli of the rubber testpieces are listed as percent retention in the Table infraand the timesto reach those retentions are recorded. Longer times indicate betterozone resistance of the rubber stock. The intermittent test comprises2-hour cycles during which the specimens are exposed dynamically of thetime and during the remainder of the time are exposed statically atstrain.

The test stock is a typical formulation of styrenebutadiene copolymerrubber. On the basis of 100 parts r'ubber, all parts being by weight, itcomprises:

Styrene-butadiene copolymer rubber I00 (SBR I500) Carbon black (HAF) 50Zinc oxide 4 Stearic acid 2 Hydrocarbon oil processing aid l0 Sulfur1.75 Morpholinothiobenzothiazolc l Antidegradant (where present) Stock 1is a control stock containing no antidegradant. Stock 2 containssymmetrical N,N-di(l,3-dimethylbutyl)-p-phenylenediamine. Stock 3contains the new N-l ,3-dimethylbutyl-N '-l,4-dimethylpentyl-pphenylenediamine. Stock 4 contains 1 part each ofN,N'-di( l ,3-dimethylbutyl)-p-phenylenediamine and Skin tests ontypical rubber compositions containing N-l ,3-dimethylbutyl-N'-l,4-dimethylpenty1-pphenyienediamine as the major antidegradant indicatesthat they are safe to use being comparable to control compositionspreserved with p-phenylenediamine antiozonants known from longexperience to be safe to use.

In general, the antidegradant of this invention is valuable for thepreservation of sulfur-Vulcanizable diene rubbers. Those containing morethan 50% diene hydrocarbon are preferred. The group of rubbers includesnatural rubbers, styrene-butadiene copolymer rubber and the variousstereospecific polymerized dienes, for example, cis-polybutadiene andcis-polyisoprene. The compositions are also useful in diene rubbers oflow unsaturation such as butyl rubber and ethylenepropylene-dieneterpolymer rubber (EPDM). The amount to use will vary depending upon theparticular formulation and the purpose of the compounder but, ingeneral, the amounts will fall within the range of 0.1 to 5% of therubber content.

Although the invention has been illustrated by typical examples, it isnot limited thereto. Changes and modifications of the examples of theinvention herein chosen for purposes of disclosure can be made which donot constitute departure from the spirit and scope of the invention.

The embodiments of the invention in which an exclusive property orprivilege is claimed are defined as follows:

1. Vulcanizable diene rubber having incorporated therein a stabilizingamount of N-l ,B-dimethylbutyl-N l,4-ditnethylpentyl-p-phenylenediamine.

2. Vulcanized diene rubber having incorporated therein a stabilizingamount of N-l ,3-dimethylbutyl-N l ,4-dimethylpentyl-p-phenylenediamine.

3. The composition of claim 2 wherein the rubber is styrene-butadienecopolymer rubber.

1. VULCANIZABLE DIENE RUBBER HAVING INCORPORATED THEREIN A STABILIZING AMOUNT OF N-1,3-DIMETHYLBUTYL-N''-4-DIMETHYLPENTYL-P-PHENYLENEDIAMINE.
 2. Vulcanized diene rubber having incorporated therein a stabilizing amount of N-1,3-dimethylbutyl-N''-1,4-dimethylpentyl-p-phenylenediamine.
 3. The composition of claim 2 wherein the rubber is styrene-butadiene copolymer rubber. 